TY - JOUR
T1 - A previously unreported type of seismic source in the firn layer of the East Antarctic Ice Sheet
AU - Lough, Amanda C.
AU - Barcheck, C. Grace
AU - Wiens, Douglas A.
AU - Nyblade, Andrew
AU - Anandakrishnan, Sridhar
N1 - Funding Information:
Data used in this study were collected as part of the GAMSEIS and TAMSEIS deployments and is available via the IRIS data management center (http://ds.iris. edu/ds/nodes/dmc). We would like to thank all members of the GAMSEIS and TAMSEIS field teams who collected the data used here as well as the IRIS data management center for maintaining the archived data. Instruments for both experiments were provided by IRIS/PASSCAL instrument center in Socorro, NM. We also want to thank Dan Bartz and Zihe Zhang for their work on initial identification of potential events. This work has been supported by National Science Foundation grants ANT-0537597, ANT-0838934, and PLR-1246712.
Publisher Copyright:
©2015. American Geophysical Union. All Rights Reserved.
PY - 2015/11/1
Y1 - 2015/11/1
N2 - We identify a unique type of seismic source in the uppermost part of the East Antarctic Ice Sheet recorded by temporary broadband seismic arrays in East Antarctica. These sources, termed "firnquakes," are characterized by dispersed surface wave trains with frequencies of 1-10 Hz detectable at distances up to 1000 km. Events show strong dispersed Rayleigh wave trains and an absence of observable body wave arrivals; most events also show weaker Love waves. Initial events were discovered by standard detection schemes; additional events were then detected with a correlation scanner using the initial arrivals as templates. We locate sources by determining the L2 misfit for a grid of potential source locations using Rayleigh wave arrival times and polarization directions. We then perform a multiple-filter analysis to calculate the Rayleigh wave group velocity dispersion and invert the group velocity for shear velocity structure. The resulting velocity structure is used as an input model to calculate synthetic seismograms. Inverting the dispersion curves yields ice velocity structures consistent with a low-velocity firn layer ~100 m thick and show that velocity structure is laterally variable. The absence of observable body wave phases and the relative amplitudes of Rayleigh waves and noise constrain the source depth to be less than 20 m. The presence of Love waves for most events suggests the source is not isotropic. We propose the events are linked to the formation of small crevasses in the firn, and several events correlate with shallow crevasse fields mapped in satellite imagery.
AB - We identify a unique type of seismic source in the uppermost part of the East Antarctic Ice Sheet recorded by temporary broadband seismic arrays in East Antarctica. These sources, termed "firnquakes," are characterized by dispersed surface wave trains with frequencies of 1-10 Hz detectable at distances up to 1000 km. Events show strong dispersed Rayleigh wave trains and an absence of observable body wave arrivals; most events also show weaker Love waves. Initial events were discovered by standard detection schemes; additional events were then detected with a correlation scanner using the initial arrivals as templates. We locate sources by determining the L2 misfit for a grid of potential source locations using Rayleigh wave arrival times and polarization directions. We then perform a multiple-filter analysis to calculate the Rayleigh wave group velocity dispersion and invert the group velocity for shear velocity structure. The resulting velocity structure is used as an input model to calculate synthetic seismograms. Inverting the dispersion curves yields ice velocity structures consistent with a low-velocity firn layer ~100 m thick and show that velocity structure is laterally variable. The absence of observable body wave phases and the relative amplitudes of Rayleigh waves and noise constrain the source depth to be less than 20 m. The presence of Love waves for most events suggests the source is not isotropic. We propose the events are linked to the formation of small crevasses in the firn, and several events correlate with shallow crevasse fields mapped in satellite imagery.
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U2 - 10.1002/2015JF003658
DO - 10.1002/2015JF003658
M3 - Article
AN - SCOPUS:84954383675
VL - 120
SP - 2237
EP - 2252
JO - Journal of Geophysical Research: Earth Surface
JF - Journal of Geophysical Research: Earth Surface
SN - 2169-9003
IS - 11
ER -